The use of industrialized agricultural technologies has expanded and grown significantly, concomitant with world population growth and the growing need for nourishment. The processing and manufacturing of mass quantities of agricultural products and crops, such as for example vegetables, fruits, meat, and diary products, results in large amounts of wastes, especially in the form of strong refractory wastewater produced in such industries. The disposal of such wastes in environmentally unsuitable and unsafe forms has caused severe ecological problems. For example, wastewater from olive mills, paper mills, meat industry, dairy industry and so forth contain very high organic load and high content of microbial growth-inhibiting compounds.
Current agro-industrial wastewater treatment technologies are based on biological (mainly anaerobic) and physico-chemical treatment systems, in which some of the effluents are disposed without any treatment. The anaerobic treatment systems involve unstable long and slow processes characterized by long start-up periods.
Although agricultural waste is considered as source of groundwater, air, landscape and nature pollution, it could be converted into environmentally and economically profitable products. The high organic matter concentration found in agricultural waste may serve as a source for biogas production under anaerobic digestion conditions.
A variety of anaerobic digestion technologies are available [Seghezzo L. et al., Bioresource Technol. 65: 175-190, 1998; Zemman, G. et al., Water Sci. Technol., 35, 121-128, 1997]. However, the anaerobic digestion processes currently used are known of their low methane gas production yields, process instability, high retention time and long start-up period.
Within the different anaerobic treatment systems studied so far, up-flow anaerobic sludge blanket (UASB) reactor is considered to be one of the most popular bioreactors to treat agro-industrial wastewaters characterized by high organic load and high efficiency of Chemical Oxygen Demand (COD) [Erguder, T. H. et al., Process Biochem, 36: 243-248, 2000]. However, the major problems involved with the UASB system are the required long-term start-up periods, instability of the biological activity, high toxicity of phenolic compounds and tannins, and the need to adjust the pH in the medium of the reactor [Sabbah, I. et al., Process Biochem, 39: 1947-1951, 2004].
Immobilization of anaerobic sludge for wastewater treatment is known in the art, however, so far limited research was conducted in the field of such immobilization [R. H. Wijffels, et al., Elsevier Science B.V. p. 98-106, 1996; M. Varesche et al., “Characterization of anaerobic biomass immobilized in polyurethane foam matrices from HAIS reactor by scanning electron microscopy”, 1996; M. Varesche et al., Appl. Microbiol Biotechnol 48, 534-538, 1997; Han Wei et al., Journal of Forestry Research, 21, 509-513, 2010; M. Zaiat et al., Wat. Res 30, 2435-2439, 1996; Ana C. T. Ramos et al., “Mass transfer improvement of a fixed-bed anaerobic sequencing batch reactor with liquid-phase circulation”, 2003]. In known immobilization processes solid matrices such as polyurethane (PU) foam matrices are immersed in anaerobic reactors and biomass can attach to the support matrix (polyurethane cube) and then growth of the biomass in the pores of the polyurethane foam occurs.